This invention relates generally to the field of vascular occlusion devices and methods. More specifically, it relates to an apparatus and method for occluding a blood vessel by embolizing a targeted site (such as an aneurysm) in the blood vessel.
The embolization of blood vessels is desired in a number of clinical situations. For example, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. In recent years, vascular embolization for the treatment of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. U.S. Pat. No. 4,819,637 xe2x80x94Dormandy, Jr. et al., for example, describes a vascular embolization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter, and it is inflated inside the aneurysm with a solidifying fluid (typically a polymerizable resin or gel) to occlude the aneurysm. The balloon is then detached from the catheter by gentle traction on the catheter. While the balloon-type embolization device can provide an effective occlusion of many types of aneurysms, it is difficult to retrieve or move after the solidifying fluid sets, and it is difficult to visualize unless it is filled with a contrast material. Furthermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon from the catheter.
Another approach is the direct injection of a liquid polymer embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, and then is polymerized in situ. Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer mixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO). Another type is ethylene glycol copolymer dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this xe2x80x9cdirect injectionxe2x80x9d method are disclosed in the following U.S. Pat. No. 4,551,132xe2x80x94Pxc3xa1sztor et al.; U.S. Pat. No. 4,795,741xe2x80x94Leshchiner et al.; U.S. Pat. No. 5,525,334xe2x80x94Ito et al.; and 5,580,568xe2x80x94Greff et al.
The direct injection of liquid polymer embolic agents has proven difficult in practice. For example, migration of the polymeric material from the aneurysm and into the adjacent blood vessel has presented a problem. In addition, visualization of the embolization material requires that a contrasting agent be mixed with it, and selecting embolization materials and contrasting agents that are mutually compatible may result in performance compromises that are less than optimal. Furthermore, precise control of the deployment of the polymeric embolization material is difficult, leading to the risk of improper placement and/or premature solidification of the material. Moreover, once the embolization material is deployed and solidified, it is difficult to move or retrieve.
Another approach that has shown promise is the use of thrombogenic microcoils. These microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase thrombogenicity. The coil is deployed through a microcatheter to the vascular site. Examples of microcoils are disclosed in the following U.S. Pat. No. 4,994,069xe2x80x94Ritchart et al.; U.S. Pat. No. 5,133,731xe2x80x94Butler et al.; U.S. Pat. No. 5,226,911xe2x80x94Chee et al.; U.S. Pat. No. 5,312,415xe2x80x94Palermo; U.S. Pat. No. 5,382,259xe2x80x94Phelps et al.; U.S. Pat. No. 5,382,260xe2x80x94Dormandy, Jr. et al.; U.S. Pat. No. 5,476,472xe2x80x94Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074xe2x80x94Mirigian; U.S. Pat. No. 5,582,619xe2x80x94Ken; U.S. Pat. No. 5,624,461xe2x80x94Mariant; U.S. Pat. No. 5,645,558xe2x80x94Horton; U.S. Pat. No. 5,658,308xe2x80x94Snyder; and U.S. Pat. No. 5,718,711xe2x80x94Berenstein et al.
The microcoil approach has met with some success in treating small aneurysms with narrow necks, but the coil must be tightly packed into the aneurysm to avoid shifting that can lead to recanalization. Microcoils have been less successful in the treatment of larger aneurysms, especially those with relatively wide necks. A disadvantage of microcoils is that they are not easily retrievable; if a coil migrates out of the aneurysm, a second procedure to retrieve it and move it back into place is necessary. Furthermore, complete packing of an aneurysm using microcoils can be difficult to achieve in practice.
A specific type of microcoil that has achieved a measure of success is the Guglielmi Detachable Coil (xe2x80x9cGDCxe2x80x9d). The GDC employs a platinum wire coil fixed to a stainless steel guidewire by a solder connection. After the coil is placed inside an aneurysm, an electrical current is applied to the guidewire, which heats sufficiently to melt the solder junction, thereby detaching the coil from the guidewire. The application of the current also creates a positive electrical charge on the coil, which attracts negatively-charged blood cells, platelets, and fibrinogen, thereby increasing the thrombogenicity of the coil. Several coils of different diameters and lengths can be packed into an aneurysm until the aneurysm is completely filled. The coils thus create and hold a thrombus within the aneurysm, inhibiting its displacement and its fragmentation.
The advantages of the GDC procedure are the ability to withdraw and relocate the coil if it migrates from its desired location, and the enhanced ability to promote the formation of a stable thrombus within the aneurysm. Nevertheless, as in conventional microcoil techniques, the successful use of the GDC procedure has been substantially limited to small aneurysms with narrow necks.
There has thus been a long-felt, but as yet unsatisfied need for an aneurysm treatment device and method that can substantially fill aneurysms of a large range of sizes, configurations, and neck widths with a thrombogenic medium with a minimal risk of inadvertent aneurysm rupture or blood vessel wall damage. There has been a further need for such a method and device that also allow for the precise locational deployment of the medium, while also minimizing the potential for migration away from the target location. In addition, a method and device meeting these criteria should also be relatively easy to use in a clinical setting. Such ease of use, for example, should preferably include a provision for good visualization of the device during and after deployment in an aneurysm.
Broadly, one aspect of the present invention is an embolic device, comprising a thrombogenic medium, that is deployed in a soft, compliant state, and that is controllably transformed into a rigid or semi-rigid state after deployment. In another aspect, the present invention is an apparatus for deploying the aforesaid embolic device in the interior of an aneurysm. Still another aspect of the present invention is a method for embolizing a vascular site, particularly an aneurysm, using the aforesaid embolic device.
In a first preferred embodiment, the embolic device comprises a continuous, filamentous extrusion of polymeric xe2x80x9ctransition materialxe2x80x9d that is inserted into an aneurysm while in a soft, self-adherent, compliant state. The insertion of one or more such embolic devices results in a mass of material that substantially fills the aneurysm and that substantially conforms to the interior shape of the aneurysm. Depending on the particular polymeric material employed, any of several mechanisms is then employed controllably to transform the transition material into a rigid or semi-rigid state, in which the material forms a stable, thrombogenic xe2x80x9cplugxe2x80x9d inside the aneurysm. For example, the material may be injected at a temperature slightly above body temperature and then cooled into its rigid or semi-rigid state by contact with the patient""s blood, or by the injection of a cooler saline solution. Alternatively, the polymeric material may be exposed to a hardening agent that reacts physically or chemically with the material to effect the transition to the rigid or semi-rigid state. As still another alternative, the polymeric material may be mixed with a water soluble, biocompatible plasticizer that dissolves out in the vascular blood to leave a rigid or semi-rigid polymeric structure.
In another preferred embodiment, the embolic device comprises an elongate, flexible microcoil, the interior of which contains the transition material. The microcoil is deployed in the aneurysm with the transition material in its soft, compliant state, and then the transition material is rigidified by any suitable mechanism, as mentioned above, thereby rigidifying the microcoil in situ.
In another preferred embodiment, the embolic device comprises an elongate, flexible chain of articulated segments linked together so as to form a limp segmented filament that is installed in the aneurysm. After placement in the aneurysm, the segmented filament is rigidized by fusing the segments through one of several mechanisms, depending on the material of the segments. For example, if the segments are metal, the segments can be fused together by electrolytic corrosion resulting from a current being passed through the device. If the segments are made, at least in part, of a polymeric xe2x80x9ctransition materialxe2x80x9d, the transition of the device to a rigid or semi-rigid state can be induced by one of the mechanisms discussed above.
In still another preferred embodiment, the embolic device is a highly-compliant chain-like structure comprising a plurality of interconnected hollow links or segments. Each of the segments has a slotted, mushroom-shaped head portion and a socket portion that is shaped and dimensioned to receive the head portion of an adjacent segment. The hollow segments allow the embolic device to be inserted into an aneurysm over a guide wire (not shown), if desired. Once the device is inserted, a polymeric transition material is injected, while in the soft, compliant state, into the hollow interior of the device, and the transformation into its rigid or semi-rigid state can be effected as described above. Alternatively, the segments can be made of a metal and then fused together by electrolytic corrosion.
A preferred embodiment of the apparatus for deploying the embolic device comprises a flexible, elongate, hollow deployment tube having an axial passage and a cup-shaped holding element at its distal end. The holding element, which is configured and dimensioned to hold the proximal end of the embolic device by a frictional engagement, has a base with an opening that communicates with the axial lumen. The deployment tube (or at least its distal end) is preferably made of a radiopaque material, such as a biocompatible metal alloy, thereby facilitating visualization during the deployment of the embolic device, without requiring the inclusion of a radiopaque substance in the embolic device itself.
The preferred method of deploying the embolic device using this apparatus is as follows: The deployment tube, with the embolic device thus attached to it, is inserted into and pushed through a microcatheter that has been advanced intravascularly to the aneurysm site by means well known in the surgical arts. Passage of the flexible deployment tube and the limp embolic device through the microcatheter is assisted and facilitated by a flow of fluid (e.g., saline solution) through the microcatheter around the exterior of the deployment tube and the embolic device. The deployment tube is pushed through the microcatheter until the embolic device has been fully inserted into the aneurysm. Finally, a fluid (e.g., saline solution) is injected through the axial lumen and into the holding element of the deployment tube. The pressure of the fluid pushes the embolic device out of the holding element, thereby detaching the embolic device from the deployment tube. The deployment tube is then withdrawn from the microcatheter. If more than one embolic device is necessary to fill the aneurysm, the above-described process can be repeated until the aneurysm is filled.
The present invention offers a number of advantages over prior art embolization methods and devices. For example, the embolic device of the present invention is deployable within an aneurysm in a soft, compliant state, thereby minimizing the risk of aneurysm rupture or vascular damage. The location of the embolic device can be controlled with some precision, and, until it is detached from the deployment tube, its deployment can be reversed. Thus, the risks of migration out of the aneurysm are minimized. Furthermore, the embolic device of the present invention can be used in aneurysms having a wide variety of shapes and sizes; it is not limited to small aneurysms or those with narrow necks. These and other advantages of the present invention will be more fully appreciated from the detailed description that follows.